1. Field of the Invention
This invention relates to a device for monitoring the freezing temperature history of a perishable product for example, vaccines, fresh produce, flowers, latex paints, emulsions such as milk, fruit juices, and yogurt, to determine if the product has been subjected to a freezing temperature and thus has been damaged.
2. Brief Description of Prior Art
There are a variety of defrost indicators reported in the literature for monitoring of thawing of perishables such as ice-cream. See U.S. Pat. Nos. 4,892,677, 5,685,641, 5,695,284 and 4,735,745, which utilize a diacetylene as an indicator. This type of indicator undergoes a color change when the product temperature undesirably exceeded about 0xc2x0 C. U.S. Pat. No. 4,892,677, to Preziosi, et al., describes a defrost indicator which is prepared by mixing a diacetylene monomer with a solvent. The mixture is frozen and irradiated in the frozen state to partially polymerize the diacetylene. Once the frozen indicator is exposed to a temperature sufficient to melt the solvent the monomer is extracted from the partially polymerized diacetylene thereby forming a polymer enriched diacetylene phase and a monomer enriched solvent phase. The device of Preziosi et al. is irreversible and unidirectional and only capable of providing a signal with an increase in temperature.
U.S. Pat. Nos. 4,191,125, 5,111,768, and 5,239,942 describe freeze indicators. These indicators usually employ a frangible glass container which contains a colored aqueous solution which ruptures upon freezing and then contacts a wick such as paper upon thawing to indicate that undesirable thawing has occurred. Other representative patents on freeze-thaw type indicators include U.S. Pat. Nos. 4,114,443, 4,145,918 4,148,748, 4,191,125, 5,111,768 and 5,239,942. These type of devices are large, complex, difficult to manufacture, and expensive.
There is a constant need in the art for a device which is simple, easy to make, does not depend upon the use of a frangible glass container, and is economical for commercial production. Especially there is a need for a device to monitor the freeze temperature of such perishable food products as described above, which become damaged and inedible if frozen.
It is an object of the present invention to provide a device which can indicate temperature excursions below a threshold temperature.
It is another object of the present invention to provide a device which irreversibly indicates a temperature excursion below a threshold temperature which can be easily prepared from readily available, inexpensive materials.
We have discovered that an aqueous solution of certain organic solvents, e.g., ethylene glycol diacetate, will undergo phase separation at the freezing point of water thus concentrating the solvent in liquid form. When the separated solvent then contacts, for example, a partially polymerized diacetylene, it can extract monomer and cause a color change in the diacetylene. Thus, one is aware that the perishable product, e.g., live virus polio vaccine, has been undesirably subjected to a freezing temperature and is possibly damaged.
By this invention there is provided a device comprising: an indicator which is capable of undergoing a color change; and an activator system. The activator system is comprised of a solution of water and an activator solvent. The activator solvent is miscible with water and capable of separating out of the solution at or below the freezing point of water thereby inducing a color change in the indicator upon contact. The indicator is in contact with the activator system and when the device is subjected to a temperature at or below the freezing point of water, sufficient solvent separates from the solution to contact the indicator and induce a color change in the indicator.
Further provided is a process for monitoring the freezing temperature history of an article comprising the step of affixing a device, as described above, to the article and comparing any change in color to a control color.
Furthermore there is provided a color indicator comprising a gel formulation comprised of: water, a water miscible solvent capable of phase separation from the water solution in the temperature range of 0 to xe2x88x9230xc2x0 C., a gelling agent and a dispersion of a partially polymerized diacetylene.
These and other advantages, as will be realized, are provided in a process for detecting temperature excursions of an article below a threshold temperature. The process comprises the steps of:
a) preparing a freeze indicator comprising an activator system and an indicator.
b) partially polymerizing said indicator at a temperature above the threshold temperature;
c) attaching the freeze indicator to the article wherein when the article is exposed to a temperature below the threshold temperature the activator solvent separates from the water and reacts with the indicator to cause a color change in the indicator. The activator system comprises water and an activator solvent which is miscible in the water above the threshold temperature and separates from the water below said threshold temperature. The indicator is capable of irreversibly reacting with said solvent when separated from said water.
Another embodiment is provided in a method for preparing an indicator for indicating an excursion below a threshold temperature comprising: mixing an indicator with a solvent system wherein the solvent system comprises a host solvent and an activator solvent and wherein the activator solvent is miscible in the host solvent above the threshold temperature and separates from the host solvent below the threshold temperature; exposing the indicator to radiation to polymerize the indicator wherein the exposing is done at a temperature above the threshold temperature; wherein when the indicator is exposed to a temperature below the threshold temperature the activator solvent separates from the host solvent and reacts with the indicator and the indicator changes color.
Yet another embodiment is provided in a method for detecting a temperature excursion of an item below a threshold temperature comprising mixing an indicator with a solvent system wherein the solvent system comprises a host solvent and an activator solvent and wherein the activator solvent is miscible in the host solvent above the threshold temperature and separates from the host solvent below the threshold temperature; exposing the indicator to radiation to polymerize the indicator wherein the exposing is done at a temperature above the threshold temperature; and attaching the indicator to the item wherein when the item is exposed to a temperature below the threshold temperature the activator solvent separates from the host solvent and reacts with the indicator and the indicator undergoes a color change.
A particularly preferred embodiment is provided in a device for detecting excursions below a threshold temperature. The device comprises a compound of the formula Rxe2x80x2xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94Rxe2x80x3; wherein Rxe2x80x2 and Rxe2x80x3 are independently selected from (CH2)bxe2x80x94H, (CH2)bOH, (CH2)bxe2x80x94OCONHxe2x80x94R1, (CH2)bxe2x80x94Oxe2x80x94COxe2x80x94R1, (CH2)bxe2x80x94OCONHCH2COOxe2x80x94R1, (CH2)bxe2x80x94COOH, (CH2)bxe2x80x94COOM, (CH2)bxe2x80x94NH2, (CH2)bxe2x80x94CONHR1, (CH2)bxe2x80x94COxe2x80x94Oxe2x80x94R1, where b=1-10, and R1 is an aliphatic or aromatic radical, and M is a cation, such as Na+ or (R1)3N+. The device further comprises a solvent system comprising a host solvent and an activator solvent. The activator solvent is miscible in the host solvent above the threshold temperature and separates from the host solvent below the threshold temperature. The compound is exposed to UV radiation above the threshold temperature to partially polymerize the compound. When the device is exposed to a temperature below the threshold temperature the activator solvent separates from the host solvent and dissolves unpolymerized compound thereby causing a color change in the partially polymerized compound.
Yet another embodiment is provided in a device for detecting excursions below a threshold temperature. The device comprises a compound of the formula Rxe2x80x2xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94Rxe2x80x3; wherein Rxe2x80x2 and Rxe2x80x3 are independently selected from (CH2)bxe2x80x94H, (CH2)bOH, (CH2)bxe2x80x94OCONHxe2x80x94R1, (CH2)bxe2x80x94Oxe2x80x94COxe2x80x94R1, (CH2)bxe2x80x94OCONHCH2COOxe2x80x94R1, (CH2)bxe2x80x94COOH, (CH2)bxe2x80x94COOM, (CH2)bxe2x80x94NH2, (CH2)bxe2x80x94CONHR1, (CH2)bxe2x80x94COxe2x80x94Oxe2x80x94R1, where b=1-10, and R1 is an aliphatic or aromatic radical, and M is a cation, such as Na+ or (R1)3N+. The device further comprises a phase system comprising a host and an activator solvent wherein the activator solvent is miscible in the host above the threshold temperature and separates from the host below the threshold temperature. The device is prepared by the process of exposure to UV radiation above the threshold temperature to polymerize the compound. When the device is exposed to temperature below the threshold temperature the activator solvent separates from the host and dissolves the polymerized compound thereby causing a color change.
Yet another embodiment is provided in a process for detecting temperature excursions of an article below a threshold temperature. The process comprises preparing a freeze indicator with a solvent phase comprising water and ethylene glycol diacetate and a diacetylene phase. The diacetylene phase is partially polymerizing at a temperature above the threshold temperature which will therefore contain monomer and polymer. The partially polymerized diacetylene phase has a first color. The freeze indicator is attached to the article and when the article is exposed to a temperature below the threshold temperature the ethylene glycol diacetate separates from the water in an amount sufficient to extract the monomer from the partially polymerized diacetylene phase thereby forming a monomer depleted diacetylene phase which has a second color.
Yet another embodiment is provided in a device for detecting a temperature excursion below a threshold temperature. The device comprises a diacetylene phase comprising polymerized diacetylene and monomeric diacetylene. The device further comprises a molten solvent phase which comprises a host solvent and an activator solvent wherein the activator solvent is miscible with the host solvent above the threshold temperature and separates from the host solvent below the threshold temperature forming an activator phase. The activator phase dissolves the monomeric diacetylene from the diacetylene phase forming a monomer depleted polymer phase which is a different color from the diacetylene phase.
Yet another embodiment is provided in a device for detecting a temperature excursion below a threshold temperature. The device comprises a diacetylene phase comprising polymerized diacetylene and monomeric diacetylene. The device further comprises a gel phase comprising a gel and an activator solvent wherein the activator solvent is miscible with the gel above the threshold temperature and separates from the gel below the threshold temperature thereby forming an activator phase. The activator phase dissolves the monomeric diacetylene from the diacetylene phase forming a monomer depleted polymer phase which is a different color from the diacetylene phase.
A particularly preferred embodiment is provided in a gel formulation for detecting temperature excursions below a threshold temperature. The gel dispersion comprises water and a solvent which is miscible with water above the threshold temperature and separates from water below the threshold temperature. A gelling agent and dispersion of partially polymerized diacetylene comprising polymerized diacetylene and monomeric diacetylene are provided to the gel formulation. When the gel formulation is exposed to temperatures below the threshold temperature the solvent separates from the water and extracts the monomeric diacetylene from the dispersion and the dispersion changes color.